Questions to Ask a Basement or Addition Contractor
Always simple. Never easy.
For finishing a basement or adding on: the intended use and approvals, moisture and radon, escape openings, the foundation and roof tie-ins, heating, power and matching what's already there.
By Clamp ResearchReviewed by Emmanuel ForgePublished Oct 17, 2026Updated Oct 17, 2026
Start with what the space will be used for, because that decides the approvals, the escape openings and the headroom. Then settle the water: a basement is finished after its moisture is solved, and an addition is only as dry as its tie-in to the old roof and walls. Several honest answers here are “we have to open it first.”
What will the space be used for, and what approvals does that need?
Intended use: write it down and find the approval path
Ask what rooms and uses are planned and whether that means a new bedroom, a separate living unit or anything else that changes the approvals. Calling a room a bonus room does not change what it is used for. Zoning, permits and the local code decide what is needed, so ask for the approval path in writing.
Write down the intended use, then find the approval path for it where the job is: permits, zoning limits, any existing-building provisions. A bedroom or a separate unit changes the requirements; the label on the plan does not.
Before signingGoes on the design agreement
Ask
Be ready to answer
What rooms and uses are we planning?
Does this count as a new bedroom or a separate unit?
What permits and zoning limits apply?
What does the approval path look like?
If it's a separate unit, how do utilities, entry and sound separation work?
A useful answer includes
A written use statement
The approval path
Identified restrictions
The answer that should make you ask again
The answer not to give
Example answer“Let's confirm whether that counts as a bedroom.”
What it leaves unconfirmed: The permitted use, zoning and project classification.
Ask for: The use statement and the approval path.
Give instead: The intended use in writing and the approvals it needs here.
Where does daylight reach, and what do the windows do to the room?
Daylight: place the windows for the room you'll live in
Check the daylight before the design is fixed: where it reaches in each new room at the times you will use it, what each window faces, and what the neighbors see in. In basements, the few windows decide which spots feel good, and every window takes a furniture wall, so place them for the room you will actually live in.
Review orientation, nearby obstructions and privacy with the client, using plans, a site visit or a daylight study where needed, and label predictions as estimates. Coordinate basement windows with their wells, drainage and escape requirements, and mark which walls stay usable for furniture.
Before signingBefore framingGoes on the design agreement
Ask
Be ready to answer
Where does daylight reach in each room, and at what times?
What does each window face, and who sees in?
Which walls stay usable for furniture?
In the basement, which spots get the light?
A useful answer includes
Window placements checked against use and privacy
The furniture walls kept
The daylight story per room
The answer that should make you ask again
The answer not to give
Example answer“It'll get plenty of light.”
What it leaves unconfirmed: Where, at what hours, and at the cost of which walls.
Ask for: The daylight and privacy checked per room before framing.
Give instead: Each room's daylight, views and privacy walked before the openings are framed.
What escape openings and headroom does the finished space need?
Egress and headroom: measure before the layout
Ask what escape openings and stair access the planned use requires, and what headroom remains once floors, beams, ducts and soffits are finished. The requirements depend on the use, whether it is a new sleeping room, and the code adopted where you live, so ask for measured sections and the local determination.
Measure the finished heights under the beams and ducts and settle the escape openings the planned use needs before the layout. The rules for existing basements and new additions differ; get the local determination.
Before framingBefore excavationGoes on the design agreement
Ask
Be ready to answer
What escape openings does the planned use require?
Does the existing window count?
What headroom remains under the beams and ducts?
What has the building department said?
Drywall, drop ceiling or open: what does each do to height and access?
From the main seating and walkways, where are the finished beams and soffits visible, and do their edges line up?
A useful answer includes
Measured sections
Opening and well details
The local determination
The answer that should make you ask again
The answer not to give
Example answer“The existing window should count.”
What it leaves unconfirmed: The opening's dimensions and the rule that applies.
Ask for: The measurements and the local determination.
Give instead: Measured sections and what the building department requires for this use.
Is a bathroom, bar or laundry going in, and what does the slab need?
Below-grade plumbing: decide before the slab is touched
Decide before the slab is touched whether a bathroom, bar or laundry is going into the basement, now or ever. Ask what a defined future plan would require under the floor, what a capped rough-in costs now, and what would still have to be built later. Whether gravity drainage works or a sewage ejector is needed is a site finding, not an assumption.
Ask about the bath, bar and laundry before pricing the basement, including someday. Scope the drain path from a defined fixture plan, determine gravity or ejector on site, and price the capped rough-in beside what would remain for later, so the client chooses with real numbers.
Before signingBefore rough-inGoes on the design agreement
Ask
Be ready to answer
Is a bathroom, bar or laundry in the plan, now or later?
Does the sewer allow gravity drainage, or is an ejector needed?
What would a capped future rough-in cost while the floor is open?
Where does the drain path run?
A useful answer includes
The under-slab plumbing scope
The gravity or ejector determination
The future rough-in priced
The answer that should make you ask again
The answer not to give
Example answer“We can always add a bathroom later.”
What it leaves unconfirmed: What later costs once the slab is finished over.
Ask for: The rough-in priced now against the cut-and-patch later.
Give instead: The drain path, the gravity-or-ejector finding, and the rough-in priced against what remains for later.
Can the house carry a second story or finished attic, and where do the stairs land?
Up instead of out: the structure and the stair
Ask for structural feasibility and a stair concept before construction pricing: what the existing foundation, walls and floor can carry is an engineering determination, not a guess from the floor plan. Ask what can be verified now, what stays unknown until opening, how the house is protected while the roof is off, and where a stair would land on both floors.
Start up-additions with an engineering review and the stair, not the rendering: what the structure can carry, what reinforcing this design needs, what cannot be known until opening, the temporary roof protection, and where a code stair lands on both floors. Price the feasibility work as its own step before anyone prices construction.
Before signingGoes on the design agreement
Ask
Be ready to answer
What can the existing structure carry, and who determines that?
What stays unknown until the roof or walls are opened?
Where does the stair land on both floors, and what does it displace?
How is the house protected while the roof is off?
Does the electrical service need to grow?
A useful answer includes
The engineering feasibility review
The stair location on both floor plans
The investigation limits and protection plan
The answer that should make you ask again
The answer not to give
Example answer“Houses get second stories all the time.”
What it leaves unconfirmed: Whether this house can, and what reinforcing it needs.
Ask for: The structural review for this house before the design is priced.
Give instead: The review, the reinforcing scope and the stair location before pricing the design.
Is the basement dry and tested for radon before it's finished?
Moisture and radon: resolve them before finishes
Ask what is known about leaks, past flooding and dampness, what gets corrected before any finishes go in, and whether the space has been tested for radon. The EPA recommends testing before converting a basement and again after major renovations. A dry day is not proof of a dry basement.
Investigate the moisture history and correct bulk water before finishing. Test for radon before conversion and plan to retest after the work. Insulation and coatings are not a fix for water coming in.
Before framingGoes on the design agreement
Ask
Be ready to answer
Has the basement leaked or flooded before?
What gets corrected before finishes go in?
Has it been tested for radon?
Will it be retested after the work?
A useful answer includes
Moisture findings
The drainage scope
Radon results and a mitigation plan where indicated
The answer that should make you ask again
The answer not to give
Example answer“It was dry at the visit, so we're fine.”
What it leaves unconfirmed: The seasonal moisture and the radon level.
Ask for: The moisture history and a radon test.
Give instead: What you found, what gets corrected first, and the radon test and retest.
What about the site could affect the addition?
Site constraints: survey, utilities and access
Ask what setbacks, easements, buried utilities, septic or sewer limits, drainage, trees and equipment routes affect the addition. Some of these need a survey or a utility locate before anyone knows. They decide where the addition can go, how big it can be and how the equipment gets in.
Locate the utilities, confirm the setbacks and easements, check septic or sewer limits and drainage, and plan the equipment route and tree protection. Get a survey where it's needed before the design is fixed.
Before excavationGoes on the design agreement
Ask
Be ready to answer
What setbacks and easements apply?
Where are the buried utilities, and the septic or sewer?
How will equipment get to the site?
Which trees need protecting?
For a manufactured home, what do the data plate and approvals allow?
A useful answer includes
A survey where needed
A site plan
Utility locates and approvals
The answer that should make you ask again
The answer not to give
Example answer“We should locate utilities and confirm where the equipment can get in.”
What it leaves unconfirmed: The property and site feasibility.
Ask for: The survey, locates and site plan.
Give instead: Locates, setbacks, the equipment route and a survey where needed.
How does the new foundation connect to the existing house?
Foundation tie-in: design it, don't assume it
Ask what investigation and design are needed to connect the new foundation and framing to the existing house, including the soil, the existing footings, movement between old and new, and any temporary support. The existing footing often can't be seen until it is dug out. The connection should come from a design, not a habit.
Investigate the existing footing and soil, get the connection designed where it needs to be, and plan the temporary support. Say what you can't know until excavation and how findings are priced.
Before excavationBefore the pourGoes on the design agreement
Ask
Be ready to answer
What do we know about the existing footing?
How will the new foundation connect to the old?
Does it need an engineered design?
What happens if the old footing isn't what you expect?
A useful answer includes
The investigation
Engineered details where needed
The inspection points
The answer that should make you ask again
The answer not to give
Example answer“We'll pin the new concrete to the old.”
What it leaves unconfirmed: Whether that connection suits this house and soil.
Ask for: The investigation and the connection design.
Give instead: What you'll investigate, the designed connection and the inspections.
How do the new roof and walls tie into the old, and how is the house protected while open?
Roof and wall tie-in: show the flashing detail
Ask how the new roof and walls connect to the existing roof, siding and water-control layers, and how the occupied house is protected from weather while it is open. The tie-in is where additions leak. What the existing layers look like often isn't known until they are opened.
Detail the roof and wall intersections with continuous flashing into the existing layers, and plan the temporary weather protection while the house is open. Say what you'll find when you open the old roof and how it is priced.
Before framingBefore orders are placedGoes on the design agreement
Ask
Be ready to answer
How does the new roof tie into the old one?
How do the new walls connect to the old water-control layers?
How is the house protected while it's open?
What happens if the old roof is in worse shape than expected?
A useful answer includes
The tie-in details
The weather protection plan
Material compatibility
The answer that should make you ask again
The answer not to give
Example answer“We'll flash it into the old roof.”
What it leaves unconfirmed: The flashing continuity and the existing layers.
Ask for: The intersection details.
Give instead: The flashing detail at each intersection and the weather plan while open.
Can the existing system heat and cool the new space?
Heating and cooling: check the load first
Ask whether the existing equipment and ducts can serve the new space, and how supply, return air and controls will work with the doors closed. Adding a couple of vents to an undersized system leaves the new room uncomfortable. A load review for the actual space settles whether to extend the system or add one.
Review the load for the new space, then decide: extend the existing system if it has the capacity, or add equipment. Plan the returns with doors closed and the controls. Price the options you would actually recommend.
Before orders are placedBefore rough-inGoes on the design agreement
Ask
Be ready to answer
Can the existing system handle the added space?
How will air return with the doors closed?
Will the new space have its own thermostat?
What are the options, and what does each cost?
A useful answer includes
A load review
Equipment data
The duct and return plan
The answer that should make you ask again
The answer not to give
Example answer“We'll add a couple of vents.”
What it leaves unconfirmed: The load, the capacity and the return path.
Ask for: The load review and the options.
Give instead: The load for the new space and the system options with prices.
Can the electrical service carry the new space?
Electrical capacity: a load calculation, not a glance at the panel
Ask what loads are being added and whether the existing service supports them, what circuits the finished space requires, and whether a panel or service upgrade is needed. Spare breaker spaces are not the same as spare capacity. The answer often needs a load calculation before it is known.
Have the electrician list the new loads and run a load calculation before committing. Spare spaces in the panel do not mean spare capacity. Price any panel or service upgrade up front.
Before rough-inGoes on the design agreement
Ask
Be ready to answer
What loads are we adding?
Does the existing service have the capacity?
What circuits does the new space need?
Will the panel or service need an upgrade?
A useful answer includes
The electrician's load assessment
A circuit schedule
An upgrade proposal where needed
The answer that should make you ask again
The answer not to give
Example answer“There are spare spaces in the panel.”
What it leaves unconfirmed: The service capacity behind the spaces.
Ask for: The load calculation.
Give instead: A load calculation, the circuit list and any upgrade priced up front.
What insulation and moisture control suit these walls and this climate?
Insulation and vapor: detail the whole assembly
Ask what insulation, air sealing and moisture control suit this foundation, this climate and the existing construction. Basement walls handle ground moisture differently from above-grade walls, and plastic behind drywall is not right everywhere. Bulk water has to be fixed first; insulation does not stop a leak.
Fix bulk water first, then detail the whole wall and floor assembly for the foundation and climate: insulation, air sealing, how it dries, and the fire protection the code requires. Don't default to plastic behind drywall.
Before framingBefore walls closeGoes on the design agreement
Ask
Be ready to answer
What insulation and moisture control suit these walls?
How does the wall dry if it gets damp?
Is there anything to fix before insulating?
What fire protection does the insulation need?
A useful answer includes
The complete wall and floor assembly
Manufacturer instructions
The local energy and fire requirements
The answer that should make you ask again
The answer not to give
Example answer“We always put plastic behind the drywall.”
What it leaves unconfirmed: Whether that layer belongs in this assembly and climate.
Ask for: The assembly detail for these walls.
Give instead: The whole assembly detailed for this foundation and climate, after the water is fixed.
Which flooring suits the basement or addition, and what goes underneath?
Below-grade flooring: check the slab before the product
Choose a floor assembly for the basement or addition based on the use and what lies beneath: slab or framed floor. Moisture, flatness and stiffness are different checks, some can only happen closer to installation, and no flooring fixes water coming in. Ask what is known now, what gets tested later, each product's limits, and the fallback if conditions don't qualify.
Say which findings exist now and which tests happen later, name the selected product's moisture limits, and give the fallback if the slab doesn't qualify. Resolve known water intrusion first. Fix the floor build-up and the heights at stairs and doors early.
Before orders are placedGoes on a customer decision
Ask
Be ready to answer
Which flooring suits this room's use and the floor beneath it?
Which checks are done now, which happen later, and what are the product's limits?
What is the fallback if the slab or floor doesn't qualify?
What will the finished height be at stairs, doors and adjoining floors?
A useful answer includes
The slab or floor condition and moisture findings
Compared materials with the prep each needs
Finished heights and transitions
The answer that should make you ask again
The answer not to give
Example answer“It's waterproof flooring, so the basement doesn't matter.”
What it leaves unconfirmed: Whether the slab beneath is within the product's moisture limits.
Ask for: The moisture check and the product's limits.
Give instead: The slab findings, the compared products and the prep each needs.
How will we finish the walls and ceilings in the basement or addition?
Wall and ceiling finishes: after the moisture plan, not instead of it
For the finished basement or addition, choose paint, wallpaper, paneling, wainscot or other wall and ceiling treatments after the underlying wall and moisture plan is settled. Ask which products suit the space's humidity, cleaning and access needs, and how finishes meet existing rooms. Record colors, sheens, surface preparation and stopping points. Don't cover an unresolved moisture problem.
Resolve substrate, backing and access before the walls close; colors and decorative selections can follow. Name the product, its extent, the prep and the service points that stay reachable. Link, don't repeat, the moisture and matching decisions.
Before framingBefore walls closeGoes on a customer decision
Ask
Be ready to answer
Which walls and ceilings will get paint, wallpaper, paneling or another finish?
Which finishes suit the confirmed wall assembly and moisture conditions here?
What colors, products, sheens and surface preparation are specified?
Where does each finish stop, and will paneling block access to anything we need to reach?
A useful answer includes
A room-by-room finish schedule
Products confirmed against the wall and moisture plan
Boundaries and access details
The answer that should make you ask again
The answer not to give
Example answer“Paneling will cover the walls nicely.”
What it leaves unconfirmed: What is behind the paneling and whether it can still be inspected.
Ask for: The finish schedule checked against the moisture plan.
Give instead: A finish schedule chosen after the moisture plan, with access kept.
Which existing finishes can be matched, and where do old and new meet?
Matching: samples and a boundary
Ask which existing siding, roofing, flooring or trim can realistically be matched, where the new and old materials meet, and what visible difference is acceptable. Weathered materials rarely match new ones exactly. Samples and an agreed boundary before ordering prevent a patch that bothers you every day.
Bring samples, mark where old and new meet, and say what will look different. Offer the alternative of replacing a larger continuous section. Get the boundary agreed before ordering.
Before orders are placedGoes on a customer decision
Ask
Be ready to answer
Which existing finishes can you match?
Where will the new and old meet?
How different will it look?
What would replacing a larger section cost?
Where does disturbed siding, trim and flashing get restored, and to what boundary?
A useful answer includes
Samples or a mockup
The transition plan
The selected scope
The answer that should make you ask again
The answer not to give
Example answer“That siding color has weathered, so the new section may show.”
What it leaves unconfirmed: The appearance and the replacement boundary.
Ask for: Samples and the marked boundary.
Give instead: Samples, the boundary and the larger-section option priced.
Take your list with you
Pick questions above with “Add to my list”. Your picks stay in this browser.
Rules on contracts, deposits, permits and building codes vary by state and town. Where an answer depends on where you live, the page says to ask what applies there.